OPENDJ-2880 Rest2Ldap as an OAuth2 Resource Server

Rest2Ldap now supports the OAuth2 Authorization standard as a Resource Server.

If an access token is provided in an Authorization header, we try to resolve it
against two types of Authorization Server
* OpenAM /tokeninfo endpoint
* RFC-7662 /token-introspect endpoint (RFC7662TokenResolver class)

These two endpoints must be configured in the json configuration file.

Rest2Ldap can also try to search the access token in the Core Token Service (CTS).
This work is done by the CTSTokenResolver class

For test purpose only, we also have a FileAccessTokenResolver which
resolve access token from local json file.

Once the access token validated, we use token content to extract a user identifier in order to perform the ldap request with proxy authz control.